1. Field of the Invention
The present invention relates to decontamination of radio-contaminated metals, and in particular to decontamination of radio-contaminated metals either by combined solvent extraction and electrowinning or by oxidative electrorefining. Of particular interest to the present invention is the remediation of radio-contaminated nickel from decommissioning of the DOE-ORO diffusion cascades in which nickel is the primary constituent. However, the decontamination art taught herein applies equally well to the recovery and decontamination of other strategic metals which can be electrowon such as copper, cobalt, chromium and iron.
2. The Prior Art
The sources of radio-contamination in diffusion barrier nickel in particular include uranium with enrichment levels above natural levels, (usually about 0.7%) and reactor fission daughter products, such as Tc, Np, Pu, and any other actinides for example. These fission daughter products are present due to a limited run of reprocessed nuclear fuel through the DOE-ORO diffusion cascades.
Various decontamination processes are known in the art, and specifically for decontamination of nickel. Nickel can be removed by selectively stripping from an acidic solution by electrowinning. See U.S. Pat. No. 3,853,725. Nickel may also be removed by liquid--liquid extraction or solvent extraction. See U.S. Pat. Nos. 4,162,296 and 4,196,076. Further, various phosphate type compounds have be used in the removal of nickel. See U.S. Pat. Nos. 4,162,296; 4,624,703; 4,718,996; 4,528,165 and 4,808,034.
It is known that metallic nickel, contaminated with fission products, could be decontaminated to remove any actinides present by direct electrorefining based on the differences in reduction potential in the electromotive force (emf) series. Actinide removal is favored by two phenomena during electrorefining. Actinides have a significantly higher reduction potential relative to nickel and they are normally won from molten salt electrolyte rather than from aqueous electrolyte. See U.S. Pat. Nos. 3,928,153 and 3,891,741, for example.
In spite of these disclosures, there remains a need for an economical and efficient method to decontaminate metals and more specifically, to separate technetium from these metals in a simple manner.